This invention relates to a method for the vacuum depositing of molten alloys of metals having vapor pressures that are different from one another, from continuously fed, large-area evaporation crucibles, by direct bombardment of the bath surface with focused electron means periodically deflected according to a pattern, and for the deposition of the alloy material on a plurality of substrates which are disposed in a field above the evaporating crucible, with the local adaptation of the energy density to the thermal economy of the molten bath.
From a publication by the Chromalloy American Corporation, New York, entitled, "High Temperature Resistant Coatings for Superalloy," by Seelig et al., it is known to coat gas turbine blades with oxidation and corrosion resistant coating of, for example, CoCrAlY and NiCoCrAlY. In this case the coating or coatings of an individual bucket must be largely homogeneous, i.e., it must not vary in composition from the beginning to the end of the depositing process. If the process is to be performed on a large industrial scale, a number of blades must be coated simultaneously in a single depositing operation. This requires evaporating crucibles of large surface area. The variations in the thicknesses of the coatings and the compositions thereof must not exceed relatively close tolerances from one substrate to the next, However, vacuum depositing processes are subject to what are known as margin effects, i.e., the thickness and composition of the coating on substrates located at the margin of the evaporating crucible generally differ from those of the substrates located in the middle. To prevent a decrease in the coating thickness towards the margin it is known to increase the "dwell time," i.e., the time which an electron beam oscillating over the bath surface spends at the ends of the crucible. However, the problem of varying alloy compositions cannot be solved by this method.
It is furthermore known from U.S. Pat. No. 3,582,529 to guide a partially focused electron beam over the entire bath surface according to a particular deflection pattern. To equalize the varying energy density at the various areas struck by the electron beam, it is recommended that the dwell time of the beam at the various impinged areas be independently variable. This, however, serves principally to compensate for the negative influence of the different angles of deflection on the beam geometry or on the size of the focal spot. The size of the focal spot itself remains unaffected or is allowed to vary as it will. For the deposition of homogeneous alloy coatings on a plurality of substrates from large-area evaporating crucibles, the known method is therefore unsuitable. Consideration must be given to the fact that, in the vaporization of an alloy, the composition of the deposited coating will depend substantially on the temperature level of the evaporating surface of the molten alloy, i.e., on the energy density, while the thickness of the deposited coating is influenced substantially by the dwell time of the electron beam on the bath surface.